docs: def field(self, name_index):
          """Get a VDField instance representing a field of the vdata.
  
          Args::
  
            name_index   name or index number of the field
  
          Returns::
  
            VDfield instance representing the field
  
          C library equivalent : no equivalent
                                                         """
  
          # Transform a name to an index number
          if isinstance(name_index, str):
              status, index = _C.VSfindex(self._id, name_index)
              _checkErr('field', status, "illegal field name: %s" % name_index)
          else:
              n = _C.VFnfields(self._id)
              _checkErr('field', n, 'cannot execute')
              index = name_index
              if index >= n:
                  raise HDF4Error("field: illegal index number")
          return VDField(self, index)